U.S. patent number 8,480,791 [Application Number 12/751,201] was granted by the patent office on 2013-07-09 for methods of manufacturing mercury sorbents and removing mercury from a gas stream.
This patent grant is currently assigned to BASF Corporation. The grantee listed for this patent is Lawrence Shore, David M. Stockwell, Pascaline H. Tran, Xiaolin D. Yang. Invention is credited to Lawrence Shore, David M. Stockwell, Pascaline H. Tran, Xiaolin D. Yang.
United States Patent |
8,480,791 |
Yang , et al. |
July 9, 2013 |
Methods of manufacturing mercury sorbents and removing mercury from
a gas stream
Abstract
Sorbents for removal of mercury and other pollutants from gas
streams, such as a flue gas stream from coal-fired utility plants,
and methods for their manufacture and use are disclosed. The
methods include injecting a sorbent consisting essentially of
recovered and separated fluid cracking catalyst particles into a
flue gas stream.
Inventors: |
Yang; Xiaolin D. (Edison,
NJ), Stockwell; David M. (Westfield, NJ), Tran; Pascaline
H. (Holmdel, NJ), Shore; Lawrence (Jerusalem,
IL) |
Applicant: |
Name |
City |
State |
Country |
Type |
Yang; Xiaolin D.
Stockwell; David M.
Tran; Pascaline H.
Shore; Lawrence |
Edison
Westfield
Holmdel
Jerusalem |
NJ
NJ
NJ
N/A |
US
US
US
IL |
|
|
Assignee: |
BASF Corporation (Florham Park,
NJ)
|
Family
ID: |
38690311 |
Appl.
No.: |
12/751,201 |
Filed: |
March 31, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100266468 A1 |
Oct 21, 2010 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11763691 |
Jun 15, 2007 |
7753992 |
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60805188 |
Jun 19, 2006 |
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Current U.S.
Class: |
95/107; 95/900;
95/134 |
Current CPC
Class: |
B01J
20/10 (20130101); B01J 20/08 (20130101); B01D
53/64 (20130101); B01J 20/103 (20130101); B01J
20/24 (20130101); B01J 20/186 (20130101); B01J
20/18 (20130101); Y10S 95/90 (20130101); B01D
2257/602 (20130101) |
Current International
Class: |
B01D
53/06 (20060101); B01D 53/64 (20060101) |
Field of
Search: |
;95/90,107,134,900,902
;423/210 ;110/203,345 ;502/60,79,400 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0043759 |
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Jan 1982 |
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EP |
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0145539 |
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Jun 1985 |
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EP |
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0271618 |
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Jun 1988 |
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EP |
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0480603 |
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Apr 1992 |
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EP |
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0484234 |
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May 1992 |
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EP |
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0930091 |
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Nov 1998 |
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EP |
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0930091 |
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Jul 1999 |
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EP |
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2124249 |
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Feb 1984 |
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GB |
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2124249 |
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Feb 1984 |
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GB |
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WO-01/85307 |
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Nov 2001 |
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WO |
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WO-2007/149837 |
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Dec 2007 |
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WO |
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Other References
"Control of Mercury Emissions From Coal-Fired Electric Utility
Boilers: Interim Report Including Errata Dated Mar. 21, 2002", EPA
Research and Development--EPA--600/R-01-109 Apr. 2002 , 346 pgs.
cited by applicant .
"Control of Mercury Emissions From Coal-Fired Electric Utility
Boilers: Interim Report Including Errata Dated Mar. 21, 2002
Appendix", Apr. 2002 , 140 pgs. cited by applicant .
"PCT Search Report", PCT/US2006/044711 Apr. 24, 2007, 3 pgs. cited
by applicant .
"PCT Search Report", PCT/US2007/071523 Nov. 23, 2007, 3 pgs. cited
by applicant.
|
Primary Examiner: Lawrence, Jr.; Frank
Attorney, Agent or Firm: Brown; Melanie L
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of priority under 35 U.S.C.
.sctn.120 to U.S. application Ser. No. 11/763,691, now issued as
U.S. Pat. No. 7,753,992, filed Jun. 15, 2007, which claims the
benefit of priority under 35 U.S.C. .sctn.119(e) to U.S.
Provisional Application Ser. No. 60/805,188, filed Jun. 19, 2006,
which are incorporated herein by reference.
Claims
What is claimed is:
1. A method of removing mercury and other pollutants from a flue
gas stream comprising injecting a sorbent consisting essentially of
recovered and separated fluid cracking catalyst (FCC) particles
into the flue gas stream.
2. The method of claim 1, wherein the FCC particles are fine
particles.
3. The method of claim 2, wherein the FCC particles contain
essentially no added metal sulfides on the surface of the
particles.
4. The method of claim 2, wherein the FCC particles have an average
particle diameter of less than about 40 microns.
5. The method of claim 4, wherein the FCC particles have an average
particle diameter in the range of about 20 microns to about 40
microns.
6. The method of claim 4, wherein the FCC particles have an average
particle diameter of less than about 20 microns.
7. The method of claim 1, wherein the FCC particles contain at
least one of zeolite, hydrous kaolin, metakaolin, sodium silicate,
silica, and alumina.
8. The method of claim 7, wherein the content of each component is
in the range from zero to 100% by weight.
9. The method of claim 7, wherein the zeolite is a y-type
zeolite.
10. The method of claim 7, wherein the FCC particles are obtained
from an intermediate stage of an FCC manufacturing process.
11. The method of claim 10, wherein the FCC particles are separated
by one or more of a centrifuge, settling and filtration.
12. The method of claim 10, wherein the FCC particles are obtained
prior to ion exchange.
13. The method of claim 10, wherein the FCC particles are obtained
after ion exchange.
14. The method of claim 10, wherein the FCC particles are obtained
prior to calcination.
15. The method of claim 10, wherein the FCC particles are obtained
after calcination.
16. The method of claim 1, wherein the flue gas stream originates
from a coal-fired boiler.
17. The method of claim 1, wherein the flue gas stream originates
from an oil-fired boiler.
18. The method of claim 1, wherein the flue gas stream originates
from municipal waste combustion.
19. The method of claim 1, wherein the flue gas stream originates
from a medical waste incinerator.
Description
FIELD OF THE INVENTION
Embodiments of the invention relate to sorbents for the removal of
pollutants such as mercury from gas streams, methods for
manufacturing sorbents and the use of sorbents in pollution
control.
BACKGROUND
Emission of pollutants, for example, mercury, from sources such as
coal-fired and oil-fired boilers has become a major environmental
concern. Mercury (Hg) is a potent neurotoxin that can affect human
health at very low concentrations. The largest source of mercury
emission in the United States is coal-fired electric power plants.
Coal-fired power plants account for between one-third and one-half
of total mercury emissions in the United States. Mercury is found
predominantly in the vapor-phase in coal-fired boiler flue gas.
Mercury can also be bound to fly ash in the flue gas.
On Dec. 15, 2003, the Environmental Protection Agency (EPA)
proposed standards for emissions of mercury from coal-fired
electric power plants, under the authority of Sections 111 and 112
of the Clean Air Act. In their first phase, the standards could
require a 29% reduction in emissions by 2008 or 2010, depending on
the regulatory option chosen by the government. In addition to
EPA's regulatory effort, in the United States Congress, numerous
bills recently have been introduced to regulate these emissions.
These regulatory and legislative initiatives to reduce mercury
emissions indicate a need for improvements in mercury emission
technology.
There are three basic forms of Hg in the flue gas from a coal-fired
electric utility boiler: elemental Hg (referred to herein by the
symbol Hg0); compounds of oxidized Hg (referred to herein the
symbol Hg2+); and particle-bound mercury. Oxidized mercury
compounds in the flue gas from a coal-fired electric utility boiler
may include mercury chloride (HgCl.sub.2), mercury oxide (Hg0), and
mercury sulfate (HgSO.sub.4). Oxidized mercury compounds are
sometimes referred to collectively as ionic mercury. This is
because, while oxidized mercury compounds may not exist as mercuric
ions in the boiler flue gas, these compounds are measured as ionic
mercury by the speciation test method used to measure oxidized Hg.
The term speciation is used to denote the relative amounts of these
three forms of Hg in the flue gas of the boiler. High temperatures
generated by combustion in a coal boiler furnace vaporize Hg in the
coal. The resulting gaseous Hg0 exiting the furnace combustion zone
can undergo subsequent oxidation in the flue gas by several
mechanisms. The predominant oxidized Hg species in boiler flue
gases is believed to be HgCl.sub.2. Other possible oxidized species
may include HgO, HgSO.sub.4, and mercuric nitrate monohydrate
(Hg(NO.sub.3).sub.2.H.sub.2O).
Gaseous Hg (both Hg0 and Hg2+) can be adsorbed by the solid
particles in boiler flue gas. Adsorption refers to the phenomenon
where a vapor molecule in a gas stream contacts the surface of a
solid particle and is held there by attractive forces between the
vapor molecule and the solid. Solid particles are present in all
coal-fired electric utility boiler flue gas as a result of the ash
that is generated during combustion of the coal. Ash that exits the
furnace with the flue gas is called fly ash. Other types of solid
particles, called sorbents, may be introduced into the flue gas
stream (e.g., lime, powdered activated carbon) for pollutant
emission control. Both types of particles may adsorb gaseous Hg in
the boiler flue gas.
Sorbents used to capture mercury and other pollutants in flue gas
are characterized by their physical and chemical properties. The
most common physical characterization is surface area. The interior
of certain sorbent particles are highly porous. The surface area of
sorbents may be determined using the Brunauer, Emmett, and Teller
(BET) method of N.sub.2 adsorption. Surface areas of currently used
sorbents range from 5 m.sup.2/g for Ca-based sorbents to over 2000
m.sup.2/g for highly porous activated carbons. EPA Report, Control
of Mercury Emissions From Coal-Fired Electric Utility Boilers,
Interim Report, EPA-600/R-01-109, April 2002. For most sorbents,
mercury capture often increases with increasing surface area of the
sorbent.
Mercury and other pollutants can be captured and removed from a
flue gas stream by injection of a sorbent into the exhaust stream
with subsequent collection in a particulate matter control device
such as an electrostatic precipitator or a fabric filter.
Adsorptive capture of Hg from flue gas is a complex process that
involves many variables. These variables include the temperature
and composition of the flue gas, the concentration of Hg in the
exhaust stream, and the physical and chemical characteristics of
the sorbent. Of the known Hg sorbents, activated carbon and
calcium-based sorbents have been the most actively studied.
Currently, the most commonly used method for mercury emission
reduction is the injection of powdered activated carbon into the
flue stream of coal-fired and oil-fired plants. Currently, there is
no available control method that efficiently collects all mercury
species present in the flue gas stream. Coal-fired combustion flue
gas streams are of particular concern because their composition
includes trace amounts of acid gases, including SO.sub.2 and
SO.sub.3, NO and NO.sub.2, and HCl. These acid gases have been
shown to degrade the performance of activated carbon. Though
powdered activated carbon is effective to capture oxidized mercury
species such as Hg+2, powdered activated carbon (PAC) is not as
effective for elemental mercury which constitutes a major Hg
species in flue gas, especially for subbituminous coals and
lignite. There have been efforts to enhance the Hg0 trapping
efficiency of PAC by incorporating bromine species. This, however,
not only introduces significantly higher cost, but a disadvantage
to this approach is that bromine itself is a potential
environmental hazard. Furthermore, the presence of PAC hinders the
use of the fly ash in the cement industry and other applications
due to its color and other properties.
As noted above, alternatives to PAC sorbents have been utilized to
reduce mercury emissions from coal-fired boilers. Examples of
sorbents that have been used for mercury removal include those
disclosed in United States Patent Application Publication No.
2003/0103882 and in U.S. Pat. No. 6,719,828. In United States
Patent Application Publication No. 2003/0103882, calcium carbonate
and kaolin from paper mill waste sludge were calcined and used for
Hg removal at high temperatures above 170.degree. C., preferably
500.degree. C.
In addition, sorbents having metal sulfides on the sorbent particle
surfaces and/or between layers of layered sorbents such as clay
particles have been provided. Examples of such sorbents are
described in U.S. Pat. No. 6,719,828 and pending, commonly assigned
U.S. patent application Ser. No. 11/290,631 filed Nov. 30, 2005. In
U.S. patent application Ser. No. 11/290,631, particles such as
bentonite, kaolin, metakaolin, fly ash, zeolite, silica, alumina
and common dirt having copper sulfide dispersed on the surface were
shown to be effective mercury sorbents.
While sorbents modified with metal sulfides have showed promising
results, the modification of the particles with a metal sulfide
requires additional manufacturing steps and reagents. There is an
ongoing need to provide improved pollution control sorbents and
methods for their manufacture, particularly sorbents that are in
abundant supply and require minimal processing.
DETAILED DESCRIPTION
Aspects of the invention include methods and systems for removal of
heavy metals and other pollutants from gas streams. In particular,
the methods and systems are useful for, but not limited to, the
removal of mercury from flue gas streams generated by the
combustion of coal. One aspect of the present invention relates to
a sorbent comprising fluid cracking catalyst particles ("FCC
particles"). The FCC particles may be obtained from the end stage
or intermediate stage of an FCC particle manufacturing process, or
alternatively, they may be generated during a fluid catalytic
cracking process that uses FCC particles and generates FCC fine
particles. In particular embodiments, the methods and systems
utilize fluid cracking catalyst fine particles, which will be
interchangeably referred to as "FCC fines" or "FCC fine particles".
The fluid cracking catalyst fine particles may be recovered and
separated from a fluid cracking catalyst manufacturing process or
recovered and separated from a fluid catalytic cracking process
that uses FCC particles and generates FCC fines. Another aspect of
the invention pertains to sorbents comprising intermediate FCC
fines, which are fine particles obtained from an intermediate step
of a fluid cracking catalyst particle manufacturing process. In
specific embodiments, zeolite-containing FCC fines and intermediate
FCC fines are provided as sorbents for the removal of mercury from
gas streams.
One or more embodiments of the invention are directed to methods of
removing mercury and other pollutants from a flue gas stream
comprising injecting a sorbent consisting essentially of recovered
and separated fluid cracking catalyst (FCC) particles into the flue
gas stream.
In another embodiment, a method of removing mercury and other
pollutants from a gas stream, for example, from the flue gases of
coal-fired and oil-fired boilers, is provided comprising injecting
a sorbent comprising recovered and separated fluid cracking
catalyst particles into the flue gas stream. In certain
embodiments, the particles are fine particles. In one or more
embodiments, the particles contain essentially no added metal
sulfides on the surface of the particles.
According to one or more embodiments, the fine particles have an
average particle diameter of less than about 40 microns, for
example, an average particle diameter of between about 20 microns
and 40 microns. In certain embodiments, the fine particles have an
average particle diameter of less than about 20 microns.
In one or more embodiments, the fluid cracking catalyst particles
contain at least one of zeolite, hydrous kaolin, metakaolin, sodium
silicate, silica and alumina. The content of each component in FCC
products can be present in an amount from zero to 100% by weight.
The zeolite content of the particles according to one or more
embodiments is less than about 90% by weight. In other embodiments,
the zeolite content of the particles is less than about 50% by
weight, and in yet another embodiment, the zeolite content is less
than about 40% by weight. The zeolite is a Y-type zeolite according
to one or more embodiments.
In certain embodiments, the zeolite particles are obtained from an
intermediate stage of a FCC particle manufacturing process.
According to one or more embodiments, the FCC particles are
obtained prior to ion exchange during the manufacturing
process.
Another aspect of the invention pertains to a method of
manufacturing a mercury sorbent comprising recovering particles
from a FCC particle manufacturing process, and packaging the
particles for shipment. In one embodiment, the particles are
recovered from an intermediate step of an FCC particle
manufacturing process. In certain embodiments, FCC particles are
recovered prior to ion exchange. According to one or more
embodiments, the FCC particles include a zeolite, for example, a
Y-type zeolite. Before describing several exemplary embodiments of
the invention, it is to be understood that the invention is not
limited to the details of construction or process steps set forth
in the following description. The invention is capable of other
embodiments and of being practiced or being carried out in various
ways.
Aspects of the invention provide improved sorbents, which may be
used to remove mercury and other pollutants from the flue gases of
coal-fired and oil-fired boilers, methods for manufacturing such
sorbents, and systems and methods utilizing these sorbents. In one
or more embodiments, the sorbents comprise FCC catalyst particles
that do not contain metal sulfides on the particle surface.
During the production of these FCC catalysts, an amount of fine
particles in the range of about 0 to 40 .mu.m in excess of that
required for good fluidization in the refinery are often generated.
Heretofore, a suitable use for these excess fine particles has not
been found, and so they are therefore land-filled, which incurs
cost for the plants. The disposal of the FCC waste by-products,
referred as FCC fines, has been a long-standing concern for FCC
manufacturing.
Thus, the use of FCC fines as a mercury removal injection sorbent
not only provides an economical sorbent for processes that require
a large volume of sorbent, but also helps solve the FCC waste
disposal issue. Furthermore, since no additional raw materials or
equipment is required to make the FCC fines sorbent, the use of FCC
fines will result in significantly reduced sorbent manufacturing
costs. From the point of view of environmental protection, this is
an ideal case in which the land fill of FCC fines is eliminated, a
sorbent is provided that removes mercury from flue gas streams, and
the use of natural resources and energy for making the sorbent is
reduced.
The terms "fluid cracking catalyst fines" or "FCC fines" are used
herein to refer to fine solid particles obtained from a fluid
cracking catalyst manufacturing process, such as described in, but
not limited to U.S. Pat. Nos. 6,656,347 and 6,673,235, and to
particles generated and separated during a fluid catalytic cracking
process that uses FCC particles. For particles formed during a
fluid catalytic cracking particles manufacturing process, the
particles may be separated during one or more intermediate stages
of the manufacturing process, or at an end stage. For example, the
particles may be separated prior to ion exchange, and these
particles may be referred to as "pre-ion exchange" particles.
Alternatively, the particles may be separated after ion exchange,
and these particles may be referred to as "ion exchanged particles"
or "post-ion exchange particles." In another embodiment, the
particles may be separated either before calcination, and may be
referred to as "pre-calcination particles" or after calcination and
may be referred to as "post-calcination particles." The terms
"intermediate fluid cracking catalyst fines" or "intermediate FCC
fines" refers to particles obtained during an intermediate stage of
a fluid cracking catalyst powder manufacturing process. FCC
catalysts containing about 15% of 0-40 .mu.m fines are used for
petroleum refining via a fluid cracking catalysis process.
Intermediate FCC fines or excess FCC fines are generated in the
processes described in U.S. Pat. Nos. 6,656,347 and 6,673,235 in
two principle ways. In the first route, pre-formed microspheres
containing a mixture of calcined kaolins are immersed in sodium
silicate solution to crystallize zeolite Y, and several percent of
excess fines are generated over and above the amount present in the
original microspheres. The fines can contain sodium form zeolite Y,
gmelinite, and leached kaolin residue. The excess material is
separated by centrifuge, settling and filtration, and then
ordinarily discarded. The second route for fines formation is
microsphere attrition during handling in the ion exchange portion
of the manufacturing processes. Ion exchange is done to replace
unwanted sodium with more desirable ions. Pneumatic transportation,
rotary calcination and stirring lead to particle-particle and
particle-wall collisions and the formation of fines. Several
percent of excess fines are generated over and above the amount
present in the required particle size distribution. The fines can
contain ammonium/rare earth-form zeolite Y and gmelinite or their
collapsed residues, and leached kaolin residue. These are also
separated by centrifuge, settling and filtration, and then
ordinarily discarded. Waste fines from the various latter stages of
the process are combined together into this single process
stream.
In one or more embodiments the catalyst fines are waste material
obtained from a point in the catalyst manufacturing procedure after
reaction to form a zeolite intermediate. In other embodiments, FCC
fines are obtained after ion exchange as, for example, waste
material from a drying step or from a calcining step. In one or
more embodiments, the fines or fine particles have an average
particle size of less than about 40 microns in diameter, for
example, an average particle size of between about 20 and 40
microns in diameter microns in diameter. In other embodiments, the
average particle size of the fine particles is less than about 20
microns in diameter.
In still other embodiments, FCC fines are obtained after the
catalyst has been used in the catalytic cracking process in the oil
refinery. The used FCC catalyst from the refinery is commonly
referred to as "equilibrium catalyst" or E-cat, and this catalyst
is of a reduced surface area and activity, and may contain
contaminant metals such nickel, vanadium, iron and copper, as well
as incremental amounts of sodium, calcium and carbon. Most of the
existing equilibrium catalyst is of a larger particle size above 40
.mu.m, typically about 80 .mu.m, but equilibrium catalyst fines are
also available. Some of the fines are nothing more than essentially
fresh FCC catalyst with a particle size less than 40 .mu.m, since
the FCC hardware has limited success at retaining these particles.
The other portion of the equilibrium catalyst fines is of a lower
surface area and activity, and these are formed by
particle-particle and particle-wall collisions during use which
leads to particle attrition and fines. The two types of fines form
a mixture that is not typically separated into its components.
These fines are found in the bottoms of the FCC main distillation
column or in collection devices such as an electrostatic
precipitator or a wet gas scrubber. A portion of the fines is also
lost to the atmosphere. The effectiveness of these materials has
not been measured but it is presently speculated that these may be
useful as a mercury adsorbent.
FCC manufacturing processes are known, and examples of
manufacturing processes for zeolite-containing FCC particles are
described in the patents cited above, as well as U.S. Pat. Nos.
3,663,165; 4,493,902 and 4,699,893, which are incorporated herein
by reference. In one embodiment, as described in U.S. Pat. No.
3,663,165, preformed microspheres are obtained by calcining a spray
dried slurry of hydrous kaolin clay at elevated temperature (e.g.,
1800.degree. F.) are suspended in an aqueous sodium hydroxide
solution together with a small amount of finely divided metakaolin
(e.g., kaolin clay calcined at 1350.degree. F.). The suspension is
aged and then heated until crystalline sodium faujasite appears in
the microspheres and sodium silicate mother liquor is formed. The
crystallized microspheres are ion-exchanged to produce a zeolitic
cracking catalyst. Fines or fine particles can be obtained either
prior to or after ion-exchange and used as a mercury sorbent as
described further below.
As noted above, additional examples of processes for manufacturing
FCC catalysts are described in commonly assigned U.S. Pat. Nos.
6,656,347 and 6,673,235, the contents of each patent being
incorporated herein by reference. In U.S. Pat. No. 6,673,235, an
FCC catalyst is made from microspheres, which initially contain
kaolin, binder, and a matrix derived from a dispersible boehmite
alumina and an ultra fine hydrous kaolin having a particulate size
such that 90 Wt % of the hydrous kaolin particle are less than 2
microns, and which is pulverized and calcined through the exotherm.
The microsphere is subsequently converted using standard in-situ Y
zeolite growing procedures to make a Y-containing catalyst.
Exchanges with ammonium and rare earth cations with appropriate
calcinations provides an FCC catalyst that contains a transitional
alumina obtained from the boehmite and a catalyst of a unique
morphology to achieve effective conversion of hydrocarbon to
cracked gasoline products with improved bottoms cracking under SCT
FCC processing. Preparation of the Such a Fluid Cracking Catalyst,
as described in U.S. Pat. No. 6,673,235, may involve an initial
step of preparing microspheres comprising hydrous kaolin and/or
metakaolin, a dispersible boehmite (Al.sub.2O.sub.3, H.sub.2O),
kaolin calcined through its characteristic exotherm and derived
from ultra fine hydrous kaolin, and a binder. The microspheres are
calcined to convert any hydrous kaolin component to metakaolin. The
calcination process transforms the dispersible boehmite into a
transitional alumina phase. The calcined microspheres are reacted
with an alkaline sodium silicate solution to crystallize zeolite Y
and ion-exchanged. The transitional alumina phase that results from
the dispersible boehmite during the preparative procedure and which
forms the matrix of the final catalyst, passivates the Ni and V
that are deposited on to the catalyst during the cracking process,
especially during cracking of heavy residuum feeds. This results in
a substantial reduction in contaminant coke and hydrogen yields.
Contaminant coke and hydrogen arise due to the presence of Ni and V
and reduction of these byproducts significantly improves FCC
operation.
In U.S. Pat. No. 6,656,347, novel zeolite microspheres are formed
which are macroporous, have sufficient levels of zeolite to be very
active and are of a unique morphology to achieve effective
conversion of hydrocarbons to cracked gasoline products with
improved bottoms cracking under SCT FCC processing. The novel
zeolite microspheres are produced by a modification of technology
described in U.S. Pat. No. 4,493,902. By using non-zeolite,
alumina-rich matrix of the catalyst derived from an ultrafine
hydrous kaolin source having a particulate size such that 90 wt. %
of the hydrous kaolin particles are less than 2 microns, and which
is pulverized and calcined through the exotherm, a macroporous
zeolite microsphere is produced. Generally, the FCC catalyst matrix
useful in the '347 patent to achieve FCC catalyst macroporosity is
derived from alumina sources, such as kaolin calcined through the
exotherm, that have a specified water pore volume.
It will be understood, of course, that the present invention should
not be limited to the above cited FCC manufacturing processes. The
techniques for manufacturing FCC catalysts referred to above, are
often referred to in the art as in-situ techniques. Other
techniques for manufacturing FCC catalysts may be utilized to
provide sorbents used for mercury capture. For example,
zeolite-containing FCC catalysts may be manufactured using a
process in which the zeolitic component is crystallized and then
incorporated into microspheres in a separate step. This type of
manufacturing process may be referred to as an incorporation
process for manufacturing FCC particles.
In one or more embodiments, the FCC fines sorbent particles
comprise a mixture of zeolite, sodium silicates, metakaolin,
silica, and alumina. In certain embodiments, the FCC particles are
composed mainly of Y zeolite and minor components of sodium
silicates, metakaolin, and additives such as silica and alumina.
Y-type zeolite FCC catalysts are produced by growing a Y-type
zeolite first from metakaolin and sodium silicate slurry, followed
by rare earth ion-exchange, spraying and calcination.
In initial experiments to determine the mercury absorption of
zeolite and FCC catalysts, these catalysts were tested for their
ability to remove mercuric ions (Hg.sup.+2) from water. The Hg
capture efficiency was significantly lower than standard activated
carbon. Several aluminosilicate minerals such as bentonite and fly
ash were tested for removing mercury in flues gas and found their
activity was also too low to be considered. When FCC fines with CuS
on the surface of the fines were tested, the sorbent activity was
good and comparable to those supported on other minerals like
bentonite. However, when FCC fines alone without any metal sulfide
on the surface of the FCC fines were injected into a flue gas
stream, both the ionic and elemental mercury capture was
acceptable. It is not presently understood which component(s) in
the FCC fines are responsible for the high Hg activity since pure
Y-type zeolite or La-exchanged Y-type zeolite gave lower Hg-capture
efficiency than the FCC fines. However, the ability to remove Hg
from flue gas by using FCC fines without additional trapping
agents, such as metal sulfide, represents a breakthrough with many
benefits as outlined above.
Without intending to limit the invention in any manner, the present
invention will be more fully described by the following
examples.
EXAMPLES
Several samples were prepared in accordance with the methods for
manufacturing sorbent substrates described above.
Comparative Example 1
FCC Fines Containing CuS
Initial experiments focused on mixing FCC fines with CuS in
accordance with methods described in U.S. patent application Ser.
No. 11/290,631. Samples were made by grinding 2.90 g of
CuSO.sub.4.5H.sub.2O and 0.97 g of CuCl.sub.2.2H.sub.2O and
separately drying and grinding a wet cake obtained from a
Fundabac.RTM. filter of an FCC manufacturing process.
The mixture of copper salts was added to 10.0 g of dried Y-zeolite,
and the mixture was thoroughly ground. To this mixture, 4.16 g of
Na.sub.2S.9H.sub.2O was added, and the mixture was ground
thoroughly. The wet paste was heated in an oven at 105.degree. C.
overnight. The dried material was ground and passed though a 325
mesh sieve. This sample is labeled as Sample D-CuS.
Example 2
Preparation of FCC Fines
A wet cake of Y-type zeolite FCC fines prior to ion exchange was
obtained from a Fundabac.RTM. filter and was dried at 105.degree.
C. overnight. This sample contained sodium silicate mother liquor
waste and had a high sodium content. A second wet cake was obtained
after lanthanum ion exchange and was dried at 105.degree. C.
overnight. Each dried sample was separately passed through a 325
mesh sieve. The first sample obtained prior to ion exchange was
labeled sample A, and the second, ion-exchanged sample was labeled
sample B. A third sample labeled CBV100 was obtained from Zeolyst
of Valley Forge, Pa. CBV100 is a 100% Y zeolite powder. This sample
was labeled CBV100. A second sample of CBV100 was ion exchanged
with La, and this sample is labeled CBV100-La. The main physical
and chemical properties of these materials are shown below.
TABLE-US-00001 TABLE 1 Physical Properties Surface Area (m.sup.2/g)
N.sub.2 Pore Volume N.sub.2 Pore Diameter Particle Size (.mu.M)
Substrate N.sub.2 ZSA Total (cc/g) (nm) D.sub.50 D.sub.90 Sample A
241 273 0.23 3.3 11.9 33.5 Sample B 204 300 0.46 6.1 22.1 70.3
CBV100 666 715 0.38 2.1 4.7 16.7 Main Chemical Composition (%)
SiO.sub.2 Al.sub.2O.sub.3 Na.sub.2O LaO Fe.sub.2O.sub.3 TiO.sub.2
K.sub.2- O MgO + CaO Sample A 56.0 27.7 14.0 0.00 0.52 0.81 0.37
0.20 Sample B 60.9 26.7 6.5 2.94 0.90 0.96 0.12 0.14 CBV100 65.3
21.6 12.6 0.00 0.03 0.01 0.01 0.20
Example 3
Initial Mercury Capture Efficiency Measurements
The mercury capture efficiency was measured by Western Kentucky
University (CISET) using an in-flight reactor. The flue gas was
produced in a coal-fired pilot plant and duct-piped into the
reactor. Mercury speciation and assay was conducted using CEM and
Ontario-hydro methods. The sorbent residence time in the reactor is
1 second, sorbent injection rate 4 lbs/MMCF, and flue gas
temperature 150.degree. C.
Mercury Capture Efficiency (%) is Defined as:
100.times.[Hg(inlet)-Hg(outlet)]/[Hg(inlet)]
Table II lists the mercury capture efficiency of a total six
sorbent samples for elemental mercury, Hg(0) and total mercury,
Hg(T)=Hg(ionic)+Hg(0). For comparison, two reference materials are
also listed: one is the current industry standard injection
sorbent, Darco-LH brominated activated carbon obtained from Norit,
and the other is BN100, which is CuS/bentonite sorbent produced at
Engelhard Elyria plant prepared in accordance with the methods
disclosed in U.S. application Ser. No. 11/291,091, filed on Nov.
30, 2005 (Now U.S. Publication No. 2007/0122327) and entitled
Methods of Manufacturing Bentonite Pollution Control Sorbent. This
sample was labeled Sample C.
TABLE-US-00002 Hg (inlet), ng/Nm.sup.3 Efficiency, % Sample Hg (T)
Hg (0) Hg (T) Hg (0) Darco-LH 6000 4780 42.6 68.0 Darco-LH (repeat
1) 8332 3930 46.2 73.6 Darco-LH (repeat 2) 5460 1915 48.3 72.5
Sample C 7818 2063 48.7 66.2 Sample D-CuS 5900 4700 42.0 37.7
Sample A 6120 4880 41.3 50.0 Sample A (repeat 1) 6028 2069 40.3
28.6 Sample A (repeat 2) 5745 2052 56.0 63.0 Sample B 7979 3429
31.6 33.5 CBV100 6320 3576 33.0 17.2 CBV100-La 6864 5657 35.1
30.1
Sample D-CuS, which was a zeolite having CuS on the surface of the
particles exhibited lower elemental mercury capture efficiency, but
a good mercury capture efficiency that is comparable to those
sorbents supported on other carriers such as bentonite. However,
compared with the two reference materials of Darco-LH and BN100,
FCC fines alone without added CuS (sample A) exhibited good
Hg-capture efficiency for both Hg(T) and Hg(0), though low value of
Hg(0). Repeat 1 of sample A exhibited lower mercury capture, but
Repeat 2 was consistent with the first sample A and comparable to
Darco-LH, an industry standard. The ion-exchanged FCC fines (sample
B) exhibited a significantly lower Hg-capture efficiency than the
samples that were obtained from the intermediate stage prior to ion
exchange. Sample B also has lower sodium and zeolite content
(ion-exchange capacity) and large particle size. To test if the
differences in zeolite content and particle size contributed to the
different performance, CBV100 was tested because it is a pure
zeolite and has much smaller particle size. The Hg-capture
efficiency of CBV100 was not better than the Sample C. As noted
above, Sample C was ion-exchanged with rare earth (lanthanum)
cations. To determine the effect of rare earth ion exchange on
mercury capture, we also ion-exchanged CBV100 with lanthanum
cations, washed and dried the sample. No significant difference was
found between the CBV100 and its La-exchanged CBV100 sample.
Example 4
Mercury Leachability Test and Results of Na--Y Aluminosilicate
Fines Adsorbent
A TCLP (Toxicity Characteristic Leaching Procedure) test was
conducted in a fixed bed reactor on Samples A and B from the above
Examples. The samples were tested as follows: 0.5 gram of each
sample was mixed with glass beads. The mixed sample was then
subjected to loading on the fixed bed. The experimental temperature
of the fixed bed was set at 150.degree. C. The Hg(0) stream with a
flow rate of 0.80 L/min and concentration at 100 ug/NM.sup.3 was
delivered to pass through the fixed bed for sorbent breakthrough
tests. The PSA SCEM was used to monitor Hg(0) and also Hg(2+)
concentrations downstream of the fixed bed until breakthrough
occurred. There was no evidence that the Hg(0) stream changed its
speciation after passing through the mixed samples in the fixed
bed. Following the fixed bed tests, the mixed samples were analyzed
via a leaching test. Samples were analyzed according to Method 1311
Toxicity Characteristic Leaching Procedure (TCLP). The sample was
dissolved in an appropriate extraction solution then agitated for
19 hours. The leaching solution was analyzed by Leeman instrument
for determination of mercury concentration.
The results show that leachable Hg is 0.03% for Sample A and 0.11%
for Sample B. With 0.03% Hg leachability, the Sample A is
classified as non-hazardous material. In other words, Sample A, a
waste product from zeolite manufacturing not only effectively
captures mercury in the flue gas, but also safely retains Hg in the
spent adsorbent.
It will be apparent to those skilled in the art that various
modifications and variations can be made to the present invention
without departing from the spirit or scope of the invention. For
example, while the sorbents disclosed herein are particularly
useful for removal of mercury from the flue gas of coal-fired
boilers, the sorbents can be used to remove heavy metals such as
mercury from other gas streams, including the flue gas of municipal
waste combustors, medical waste incinerators, and other Hg-emission
sources. Thus, it is intended that the present invention cover
modifications and variations of this invention provided they come
within the scope of the appended claims and their equivalents.
* * * * *